Seat belt retractor system

ABSTRACT

A seat belt retractor system and a method of controlling the seat belt retractor system. The seat belt is retracted at a faster rate when a threat is detected using a high-voltage generated by a local power source.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a seat belt retractor system for amotor vehicle and a method of controlling a seat belt retractor system.

2. Background Art

Motor vehicles include seat belts for securing vehicle occupants. A seatbelt retractor system may be used to actuate a seat belt to eliminateslack. Actuation of the seat belt may be accomplished by use of anelectric motor. More specifically, a constant amount of voltage may beprovided to rotate the motor and retract the seat belt at a constantrate. Larger motors and 42 volt vehicle electrical systems have beenproposed to more rapidly retract a seat belt. Larger motors areundesirable due to their size and cost. 42 volt electrical systems areundesirable due to increased costs, complexity, as well as the need toredesign the entire vehicle electrical system.

Before Applicants' invention, a seat belt retractor system was neededthat could retract a seat belt at one or more increased rates. Inaddition, a seat belt retractor system and a method of control wasneeded that could provide faster actuation, yet be compatible withconventional vehicle electrical systems. In addition, a system andmethod was needed that employed standard components and did not requireadditional package space. In addition, a system and method that wasneeded that could be easily implemented in high volumes and becompatible with vehicle assembly operations. Problems associated withthe prior art as noted above and other problems are addressed byApplicants' invention as summarized below.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a seat belt retractorsystem for a vehicle is provided. The vehicle includes a vehicle safetysystem adapted to provide a signal indicative of potential injury to avehicle occupant. The seat belt retractor system includes a seat belt, aretractor mechanism, and a control circuit. The retractor mechanism isdisposed proximate the vehicle and has a motor adapted to retract theseat belt. The control circuit controls operation of the motor and isconnected to first and second voltage sources. The first voltage sourceprovides less voltage than the second voltage source. The motor isdriven by the second voltage source to retract the seat belt when thesignal provided by the vehicle safety system is indicative of a givenlevel of potential injury to the vehicle occupant. The second voltagesource is charged by the first voltage source when the signal is notindicative of a given level of potential injury to the vehicle occupant.

A charge pump may be configured to step up voltage provided by the firstvoltage source to charge the second voltage source. The charge pump mayact as a current limiter to inhibit drawing an increased level ofcurrent from the vehicle electrical system when the motor is driven bythe second voltage source. The second voltage source may be a capacitor.

The vehicle may include first and second vehicle safety systems adaptedto provide first and second signals, respectively. The control circuitmay provide voltage at a first elevated voltage level when the firstsignal is indicative of potential injury to the vehicle occupant and mayprovide voltage at a second elevated voltage level when the secondsignal is indicative of potential injury to the vehicle occupant.

According to another aspect of the present invention, a method ofcontrolling a seat belt retractor system for a motor vehicle isprovided. The motor vehicle has a vehicle safety system. The seat beltretractor system has a seat belt, a motor adapted to retract the seatbelt, and first and second voltage sources adapted to power the motor.The method includes the steps of generating a first signal indicative ofa state of charge of the second voltage source, generating a secondsignal indicative of a status of the vehicle safety system, anddetermining whether to provide power to the motor with the first voltagesource or the second voltage source to retract the seat belt based onthe first and second signals.

Power may be provided to the motor with the first voltage source whenthe state of charge of the second voltage source is less than apredetermined voltage level, when the second signal is not indicative ofpotential injury to a vehicle occupant or when the motor is activated byanother vehicle system. Power may be provided to the motor with thesecond voltage source when the state of charge of the second voltagesource is greater than a predetermined voltage level and the secondsignal is indicative of potential injury to a vehicle occupant. Thesecond voltage source may provide power for a predetermined period oftime and/or until stalling of the motor is detected.

The second voltage source may be charged with the first voltage sourcewhen the second signal is not indicative of potential injury to avehicle occupant.

According to another aspect of the present invention, a method ofcontrolling a seat belt retractor system for a motor vehicle isprovided. The motor vehicle has first and second vehicle safety systems.The seat belt retractor system has a seat belt, a motor adapted toretract the seat belt, and a control circuit adapted to control voltageprovided to the motor.

The method includes the steps of generating first and second signalsindicative of a status of the first and second vehicle safety systems,driving the motor at a first elevated voltage level to retract the seatbelt at a first elevated rate when the first signal is indicative ofpotential injury to a vehicle occupant, and driving the motor at asecond elevated voltage level to retract the seat belt at a secondelevated rate when the second signal is indicative of potential injuryto a vehicle occupant. The first elevated rate may be less than thesecond elevated rate.

The motor may be driven at the first or second elevated voltage levelsfor a predetermined period of time or until stalling of the motor isdetected.

The seat belt retractor system may include a capacitor. The step ofdriving the motor at the second elevated voltage level may includedetermining a state of charge of the capacitor and driving the motor atthe second elevated voltage level when the state of charge exceeds apredetermined voltage level. The capacitor may be charged by a voltagesource when the first and second signals are not indicative of potentialinjury to a vehicle occupant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a vehicle having a seat belt retractor system.

FIG. 2 is a schematic of one embodiment of a circuit diagram of a seatbelt retractor system.

FIG. 3 is a schematic of another embodiment of a circuit diagram of aseat belt retractor system.

FIG. 4 is a schematic of an embodiment of a circuit diagram of a chargepump for the circuit shown in FIG. 3.

FIG. 5 is a flowchart of one embodiment of a method of controlling aseat belt retractor system.

FIG. 6 is a flowchart of another embodiment of a method of controlling aseat belt retractor system.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Referring to FIG. 1, a schematic of a vehicle 10 is shown. The vehicle10 may be of any suitable type, such as a car or truck. The vehicle 10may include a seat belt retractor pretensioner system 12, one or morevehicle safety systems 14, and one or more control modules 16.

The seat belt retractor pretensioner system 12 is configured to retracta seat belt to help secure a vehicle occupant 18. The seat beltretractor pretensioner system 12 may have any suitable configuration. Inthe embodiment shown, the seat belt retractor system pretensioner 12includes a seat belt 20 and a retractor mechanism 22.

The seat belt 20 includes first and second ends. The first end may beattached to an anchor point disposed proximate the vehicle 10. Thesecond end may be attached to the retractor mechanism 22.

The retractor mechanism 22 is disposed proximate the vehicle 10 and isadapted to selectively actuate the seat belt 20. In the embodimentshown, the retractor mechanism 22 includes a spool 24 and a motor 26.

The spool 24 receives the second end of the seat belt 20 and is adaptedto rotate about an axis of rotation. More specifically, the seat belt 20is protracted or unwound from the spool 24 when the spool 24 is rotatedin a first direction and retracted or wound onto the spool 24 whenrotated in a second or opposite direction.

The motor 26 is adapted to rotate the spool 24. The motor 26 may be ofany suitable type, such as a DC motor. Moreover, the motor 26 may beconfigured with brushes, contacts, and/or internal wiring that arecompatible with a conventional 12 volt vehicle electrical system and/ora higher level of voltage, such as a 42 volt voltage source.

Optionally, the retractor mechanism 22 may include various other devicesto inhibit rotation of the spool 24. For example, the retractormechanism 22 may include a ratchet associated with the spool 24 and apawl adapted to engage the ratchet to inhibit rotation of the spool 24.In addition, a spring may be provided that provides a biasing force toretract the seat belt 20 when the motor 26 is not engaged.

The vehicle safety system 14 is adapted to predict or detect situationshaving an elevated likelihood of injury to a vehicle occupant 18. Thevehicle safety system 14 may be of any suitable type, such as an impactdetection system 30, a collision warning system 32, a vehicle dynamicssystem 34, and/or a vehicle braking system 36. Each vehicle safetysystem 14 may be adapted to activate the seat belt retractorpretensioner system 12 as well as other occupant protection systems,such as one or more front airbags, side airbags, side curtain airbags,or inflatable knee bolsters.

The impact detection system 30 is adapted to detect a collision orimpact with the vehicle 10. Impact detection systems are commonlyutilized to deploy airbags to protect vehicle occupants. Such systemsmay employ a plurality of sensors that detect a front, side, or rearimpact with the vehicle. For instance, the impact sensors may be adaptedto detect load forces, pressure, or acceleration associated with avehicle impact event. The impact sensors may be of any suitable typesuch as piezoelectric, piezoresistive, solid state, capacitive, orsilicon micromachine devices.

The collision warning system 32 is configured to detect a potentialcollision or impact with the vehicle 10 before it occurs. The collisionwarning system 32 may be of any suitable type. For instance, thecollision warning system may be radar, lidar, vision-based, or anycombination of these technologies.

The vehicle dynamics system 34 is adapted to detect vehicle instabilitysituations, such as a vehicle rollover or loss of tire pressure that mayresult in a vehicle rollover. For instance, the vehicle dynamics system34 may be a rollover sensing system having a plurality of sensors thatdetect translation and/or rotation of the vehicle or a tire pressuremonitoring system.

The vehicle braking system 36 is configured to engage vehicle brakes toreduce the velocity of the vehicle 10. The vehicle braking system 36 mayinclude a brake pedal and a brake pedal position sensor 38. The brakepedal position sensor 38 may generate a signal indicative of themagnitude and/or rate of actuation of a brake pedal by the vehicleoccupant 18. Brake pedal actuation having a sufficiently high rateand/or magnitude may be indicative of a potential vehicle impact or lossof control.

The control modules 16 are adapted to monitor and control the operationof various vehicle components and subsystems. For example, one or morecontrol modules may control or communicate with the seat belt retractorpretensioner system 12 and the vehicle safety systems 14.

Referring to FIGS. 2 and 3, circuit diagrams are shown for the seat beltretractor pretensioner system 12. The circuits are configured toselectively provide different discrete voltage levels to the motor,thereby providing different motor speeds. The motor will operate at ahigher speed when provided with a higher voltage, as long as the voltageprovided is within the motor's operational limits. Higher motor speedwill result in more rapid seat belt retraction.

Rapid seat belt retraction is desirable in situations that may result inpotential injury to a vehicle occupant. More specifically, rapidactuation of the seat belt helps prevent an occupant from moving out ofposition (e.g., closer to a window or interior trim panel). As a result,more time is available to deploy an occupant protection device, such asan airbag. In addition, rapid seat belt actuation provides more time fora collision detection system to assess potential impact situations.

Referring to FIG. 2, one embodiment of a circuit diagram is shown. Inthis embodiment, voltage may be provided at a system voltage level or ata first elevated voltage level that exceeds the system voltage level todrive the motor. The circuit 40 is connected to a vehicle electricalsystem or first voltage source 42, designated V_(in), that provides anominal or system voltage level. For example, the nominal or systemvoltage level may be approximately 12 volts.

The circuit 40 may have any suitable configuration. In the embodimentshown, the circuit 40 includes first and second branches 44,46 that areconfigured to selectively provide voltage to the motor 26.

The first parallel branch 44 may include a first switch 50 and a diode52. The first switch 50 may be any suitable type, such as a relay ortransistor. Control logic may be used to control operation of the firstswitch 50 in a manner known by those skilled in the art.

The second parallel branch 46 may include a second switch 54 and asecond voltage source 56. In addition, the second parallel branch 46 mayinclude a voltage increasing device, such as a transformer or chargepump 58.

The second switch 54 may be of any suitable type, such as a relay ortransistor. In one embodiment, a MOSFET (Metal Oxide Semiconductor FieldEffect Transistor) is employed due to its appreciable current carryingcapability, off-state voltage blocking capabilities, and low on-statevoltage drop.

The second voltage source 56 is configured to provide a higher voltagelevel than the first voltage source 42. The second voltage source 56 maybe of any suitable type. In the embodiment shown in FIG. 2, the secondvoltage source 56 is a capacitor. Alternatively, a battery or othervoltage source may be employed.

The charge pump 58 may be adapted to provide a higher output voltagethan the first voltage source 42. More specifically, the charge pump 58is adapted to step up the input voltage (V_(in)) by a predeterminedamount, such as by a factor of two or more. In the embodiment shown, theincreased voltage is provided to charge the second voltage source 56when the second switch 54 is open. Charging may be completed in a shortperiod of time, such as within a few seconds. The charge pump 58 may nothave sufficient current to drive the motor 26. In addition, the chargepump 58 may act as a current limiter to prevent activation of the motor26 from drawing excess power from the vehicle electrical system, whichwould result in voltage drops in other parts of the vehicle 10.

Operation of the embodiment of the circuit shown in FIG. 2 will now besummarized. Voltage is provided to charge the second voltage source 56and no voltage is provided to drive the motor when the first and secondswitches 50,54 are open. Voltage is provided to the motor 26 by thefirst voltage source 42 when the first switch 50 is closed and thesecond switch 54 is open. Voltage is provided to the motor 26 by thesecond voltage source 56 when the second switch 54 is closed. Moreover,the diode 52 inhibits power from flowing through the first branch 44when the first and second switches 50,54 are closed.

Referring to FIG. 3, another embodiment of a circuit diagram is shown.In this embodiment, voltage may be provided at a system voltage level, afirst elevated voltage level, or a second elevated voltage level todrive the motor at a low or “system” rate, an “intermediate” or firstelevated rate, and a “high” or second elevated rate, respectively. Ofcourse, the present invention also contemplates embodiments having anysuitable number of additional voltage levels.

The circuit 60 shown in FIG. 3 includes a first voltage source 62 andfirst, second, and third branches 64,66,68 that are configured toselectively provide voltage to the motor 26. The first branch 64includes a first switch 70 and a diode 72 like that shown in FIG. 2. Thesecond branch 66 may include a second switch 74 and a second voltagesource 76. Similarly, the third branch 68 may include a third switch 78and a third voltage source 80. In the embodiment shown, the second andthird voltage sources 76,80 are configured as capacitors.

The second and third branches 66,68 may receive voltage from a circuitor device that provides a plurality of voltages, such as a charge pump82. The charge pump 82 may have any suitable configuration. Oneexemplary embodiment of a charge pump 82 adapted to provide two outputvoltage levels is shown in FIG. 4. In this exemplary embodiment, theoutput voltages for the second and third branches are two times V_(in)(designated “2 V_(in)”) and four times V_(in) (designated “4 V_(in)”),respectively. The operation of the charge pump involves alternatelyapplying a negative charge to one side of a capacitor and a positivecharge to the other side, effectively summing them together. In FIG. 4,the capacitor (C1) shuttles power to the “reservoir capacitor” (C2)which is typically much larger than C1 and holds the final charge. Theswitches alternate between the state shown (state 1) and an alternatestate (state 2) in which all the switches are reversed from thepositions shown in FIG. 4. Different output voltage levels may beprovided by selecting appropriate circuit components in a manner knownby those skilled in the art.

The first voltage source 62 provides a low or system voltage level. Thesecond voltage source 76 may be configured to provide an intermediate orfirst elevated voltage level that is greater than the system voltagelevel. The third voltage source 80 may be configured to provide a highor second elevated voltage level that exceeds the first elevated(intermediate) voltage level provided by the second voltage source 76.

The second and third branches 66,68 may be connected to a voltageincreasing device, such as a transformer or charge pump 82 that mayprovide different output voltages to the second and third branches66,68. Alternatively, individual charge pumps that provide differentoutput voltages may be associated with both the second and thirdbranches 66,68.

Operation of the embodiment of the circuit shown in FIG. 3 will now besummarized. Voltage is provided to charge the second and third voltagesources 76,80 and no voltage is provided to drive the motor 26 when thesecond and third switches 74, 78 are open. Voltage is provided to themotor 26 by the first voltage source 62 when the first switch 70 isclosed and the second and third switches 74, 78 are open. Voltage isprovided to the motor 26 by the second voltage source 76 when the secondswitch 74 is closed and the third switch 78 is open. Voltage is providedto the motor 26 by the third voltage source 80 when the third switch 78is closed. The diode 72 inhibits power from flowing through the firstbranch 64 when the first switch and the second or third switches 74, 78are closed.

Referring to FIGS. 5 and 6, flowcharts depicting methods of controllingoperation of a seat belt retractor system are shown. As will beappreciated by one of ordinary skill in the art, the flowchartrepresents control logic which may be implemented using hardware,software, or combination of hardware and software. For example, thevarious functions may be performed using a programmed microprocessor.The control logic may be implemented using any of a number of knownprogramming or processing techniques or strategies and is not limited tothe order or sequence illustrated. For instance, interrupt orevent-driven processing may be employed in real-time controlapplications, rather than a purely sequential strategy as illustrated.Likewise, pair processing, multitasking, or multi-threaded systems andmethods may be used to accomplish the objectives, features, andadvantages of the present invention.

This invention is independent of the particular programming language,operating system processor, or circuitry used to develop and/orimplement the control logic illustrated. Likewise, depending upon theparticular programming language and processing strategy, variousfunctions may be performed in the sequence illustrated at substantiallythe same time or in a different sequence while accomplishing thefeatures and advantages of the present invention. The illustratedfunctions may be modified or in some cases omitted without departingfrom the spirit or scope of the present invention.

Referring to FIG. 5, a first embodiment of the method will be describedwith reference to the circuit shown in FIG. 2.

At 100, the method begins by determining the status of one or morevehicle safety systems. A status signal may be provided by a safetysystem directly or via an associated control module. For example, acollision, potential collision, rollover, tire deflation, high brakeactuation, or similar conditions may be indicated by the status signal.

At 102, a state of charge of a voltage source may be determined. Forexample, for the circuit shown in FIG. 2, the voltage available from thesecond voltage source 58 may be assessed. The voltage may be determinedor derived using various types of sensors in a manner known by thoseskilled in the art. This step is optional and may be omitted inalternate embodiments of the present invention.

At 104, the status signal discussed in block 100 is evaluated using athreat assessment algorithm of any type to determine if there is athreat or situation that may result in potential injury to a vehicleoccupant. For instance, the status signal may be communicated via avehicle digital communication bus, such as high-speed CAN, to indicate athreat. If the status signal is not indicative of a threat, then themethod returns to block 100. If the status signal is indicative of athreat, then the method continues at block 106.

At 106, the method may assess the voltage available from one or morevoltage sources. More particularly, the state of charge of one or morevoltage sources may be compared to a predetermined voltage level. Thepredetermined voltage level may be greater than system input voltage,V_(in). This step is optional and may be omitted. If the state of chargeis not greater than the predetermined voltage level, then the methodcontinues at block 108. If the state of charge is greater than thepredetermined voltage level, then the method continues at block 110.

At 108, the motor may be driven at a low or system voltage level. Moreparticularly, the first switch 50 is closed to provide the systemvoltage to the motor. This step provides a safing function in thatvoltage is not provided by the second voltage source if the secondvoltage source is depleted or cannot otherwise provide a higher level ofvoltage than the system input voltage. As such, this step safeguardsagainst situations in which the motor would be driven at a slower ratethan the rate associated with the vehicle electrical system.

At 110, the motor is driven at a first elevated voltage level. Morespecifically, the second switch 54 may be closed to permit the secondvoltage source to power the motor at a higher voltage level than isavailable from the vehicle electrical system. The second switch 54 mayremain closed for a predetermined period of time or may remain closeduntil stalling of the motor is detected. Motor stalling may be detectedin various ways, such as by detecting current spikes or decreasedrotation of the motor, or spool in a manner known by those skilled inthe art.

Referring to FIG. 6, another embodiment of the method is shown. Thisembodiment may be employed with a vehicle having multiple vehicle safetysystems. For convenience, this embodiment will be described withreference to the circuit shown in FIG. 3, which is configured to providevoltage at the system (low) voltage level, first elevated (intermediate)voltage level, and second elevated (high) voltage level to drive themotor. The present invention is scalable and also contemplatesembodiments having additional voltage levels.

At 200, the method begins by determining the status of a plurality ofvehicle safety systems or safety system groups. For convenience inreference, a first vehicle safety system or group of vehicle safetysystems is designated VSS₁ and a second vehicle safety system or groupof vehicle safety systems is designated VSS₂. Each safety system orgroup of vehicle safety systems may provide a status signal as describedabove with reference to block 100. For convenience in reference, theterm “vehicle safety system” is used to designate a vehicle safetysystem or a vehicle safety system group.

The concept of vehicle safety system groups will now be described ingreater detail. Different threats pose different potential risks to avehicle or vehicle occupant. For instance, a high speed frontal impactmay be associated with a higher likelihood of injury that a loss of tirepressure. Such threats may also be associated with different amounts oftime available to take corrective or protective actions, such asretracting a seat belt or deploying an airbag. As a result, threats orsituations having similar characteristics, such as available responsetime, may be organized into groups. Each group may include one or moresituations or vehicle safety systems. For example, a low speedcollision, predicted collision, loss of tire pressure, detection of avehicle rollover, or high lateral acceleration forces may be members ofa first group, while a high speed collision, a side impact event, orhigh level of brake actuation may be members of a second group. Oneskilled in the art will also recognize that different threatcombinations or additional groups may be formed. Each group may beassociated with a different seat belt retraction rate. For instance, theseat belt may be retracted at a fast rate if an event in the secondgroup is detected and may be retracted at an intermediate rate if anevent in the first group is detected.

At 202, the state of charge of one or more voltage sources may bedetermined. For example, in the circuit shown in FIG. 3, the voltageavailable from the second and third voltage sources 76,80 may beassessed as previously described. This step is optional and may beomitted in various alternate embodiments of the present invention.

At 204, the status of the second vehicle safety system or second safetysystem group, designated VSS₂, is evaluated in a manner similar to thatdescribed above with reference to block 104. For instance, a signalprovided by the second vehicle safety system or each member of thesecond safety system group, designated a VSS₂ status signal, may beassessed. If the VSS₂ status signal is not indicative of a threat, thenthe method continues at block 206. If the VSS₂ status signal isindicative of a threat, then the method continues at block 208.

At 206, the status of the first vehicle safety system or first safetysystem group, designated VSS₁, is evaluated. The signal provided by thefirst vehicle safety system or each member of the first safety systemgroup is designated the VSS₁ status signal. If the VSS₁ status signal isnot indicative of a threat, then the method returns to block 200. If theVSS₁ status signal is indicative of a threat, then the method continuesat block 210.

At 208, the state of charge of the voltage source 80 having the highestvoltage (the third voltage source in the embodiment shown in FIG. 3) maybe compared to an associated predetermined voltage level. Similar toblock 202, this step is optional and may be omitted and the method mayproceed directly to block 212. The predetermined voltage levelassociated with the third voltage source is greater than system inputvoltage, V_(in). If the state of charge is not greater than thepredetermined voltage level, then the method continues at block 210. Ifthe state of charge is greater than the predetermined voltage level,then the method continues at block 212 where the third switch 78 isclosed and the motor is driven at a fast rate. Moreover the step ofdriving the motor at a fast or second elevated rate may take precedenceover a command to drive the motor at a lower rate, such as the firstrate provided by the system voltage level or the first elevated rateprovided by the first elevated (intermediate) voltage level discussedbelow in block 214. The third switch 78 may remain closed for apredetermined period of time or until stalling of the motor is detected.

At 210, the state of charge of the intermediate voltage source 76 (thesecond voltage source in the embodiment shown in FIG. 3) may be comparedto a second predetermined voltage level. Similar to block 202, this stepis optional and may be omitted. The second predetermined voltage levelis greater than system input voltage (V_(in)) and less than the firstpredetermined voltage level associated with the third voltage source. Ifthe state of charge is greater than the second predetermined voltagelevel, then the method continues at block 214 where the second switch 74is closed and the motor is driven by the second voltage source at anintermediate rate. The second switch 74 may remain closed for apredetermined period of time or until stalling of the motor is detected.If the state of charge is not greater than the second predeterminedvoltage level, then the method continues at block 216 where the firstswitch 70 is closed and the motor is driven at a slow rate. Block 216provides a safing function by providing the system input voltage whenhigher levels of voltages are not provided by the second and thirdvoltage sources due to various reasons.

The present invention retracts the seat belt at a faster rate when suchfaster actuation is desirable. Otherwise, the seat belt is normallyactuated as a slow rate so as not to potentially alarm or causediscomfort to the seat occupant. In addition, slow actuation occursunder less severe activation conditions to reduce stress on the motor,thereby increasing operational life and reliability.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

1. A method of controlling a seat belt retractor system for a motorvehicle having a vehicle safety system, the seat belt retractor systemhaving a seat belt, a motor adapted to retract the seat belt, and firstand second voltage sources adapted to power the motor, the methodcomprising: generating a first signal indicative of a state of charge ofthe second voltage source; generating a second signal indicative of astatus of the vehicle safety system; and determining whether to providepower to the motor with the first voltage source or the second voltagesource to retract the seat belt based on the first and second signals.2. The method of claim 1 wherein power is provided to the motor with thefirst voltage source when the state of charge of the second voltagesource is less than a predetermined voltage level or the second signalis not indicative of potential injury to a vehicle occupant.
 3. Themethod of claim 1 further comprising providing power to the motor withthe second voltage source when the state of charge of the second voltagesource is greater than a predetermined voltage level and the secondsignal is indicative of potential injury to a vehicle occupant.
 4. Themethod of claim 3 wherein power is provided to the motor by the secondvoltage source for a predetermined period of time.
 5. The method ofclaim 3 wherein power is provided to the motor by the second voltagesource for a predetermined period of time or until stalling of the motoris detected.
 6. The method of claim 1 wherein the second voltage sourceis charged with the first voltage source when the second signal is notindicative of potential injury to a vehicle occupant.
 7. The method ofclaim 1 wherein the vehicle safety system is an impact detection system.8. The method of claim 1 wherein the vehicle safety system is acollision warning system.
 9. The method of claim 1 wherein the vehiclesafety system is a vehicle dynamics system adapted to detect instabilityof the vehicle.
 10. The method of claim 1 wherein the vehicle safetysystem is a vehicle brake system and the second signal is based onactuation of a brake pedal.
 11. A method of controlling a seat beltretractor system for a motor vehicle having first and second vehiclesafety systems, the seat belt retractor system having a seat belt, amotor adapted to retract the seat belt, and a control circuit adapted tocontrol voltage provided to the motor, the method comprising: generatingfirst and second signals indicative of a status of the first and secondvehicle safety systems, respectively; driving the motor at a firstelevated voltage level to retract the seat belt at a first elevated ratewhen the first signal is indicative of potential injury to a vehicleoccupant; and driving the motor at a second elevated voltage level toretract the seat belt at a second elevated rate when the second signalis indicative of a potential injury to a vehicle occupant.
 12. Themethod of claim 11 wherein the first elevated rate is less than thesecond elevated rate.
 13. The method of claim 11 wherein the motor isdriven at the first or second elevated voltage levels for apredetermined period of time or until stalling of the motor is detected.14. The method of claim 11 wherein the seat belt retractor systemfurther comprises a capacitor and the step of driving the motor at thesecond elevated voltage level further comprises determining a state ofcharge of the capacitor and driving the motor at the second elevatedvoltage level when the state of charge exceeds a predetermined voltagelevel.
 15. The method of claim 11 wherein the seat belt retractor systemfurther comprises a voltage source and the capacitor is charged by thevoltage source when the first and second signals are not indicative ofpotential injury to a vehicle occupant.